Lesson: Natural Selection
Vocabulary Words and Definitions
1. Allele
Different versions of the same gene at a given location (locus) on the DNA.
2. Environment:
In terms of natural selection the environment includes the climate, soil, food supply,
pesticides, and all the other organisms which compete with, prey on, or otherwise affect the
survival of an organism. This includes organisms of the same species.
3. Evolution:
A change in the gene pool of a population over time.
4. Gene pool:
The gene pool is the set of all genes in a species or population.
5. Genetic variability:
Differences in the genetic makeup of organisms resulting from mutation or recombination
of DNA.
6. Mutation:
A change in a gene. A mutation may change one base pair on the DNA of an
organism (a point mutation) or may involve addition or deletion of whole lengths of
DNA. Genes or parts of genes may also be duplicated and added to the DNA.
Mutations occur at random with respect to their usefulness to an organism. Most
mutations are slightly bad for the organism or neutral in effect, a very few turn out to be
mutations which positively effect an organisms ability to survive in a given
environment.
7. Natural selection:
When genetic variation exists, some genotypes increase reproduction and survival
more than others in a given environment. As the environment changes, new traits (new
combinations of alleles) will be selected for. The genotype selected by the environment will
become more common in following generations.
8. Population:
Members of a species located in the same location so they may interbreed freely.
9. Recombination:
Recombination is a shuffling of the genes which occurs through the meiosis.
Recombination occurs not only between genes, but within genes as well. Recombination
within a gene can form a new allele. Recombination is a mechanism of evolution because it adds
new alleles and combinations of alleles to the gene pool.
10. Species:
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A group of plants or animals that would be able to breed if they were at the same
location.
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Notes to the Teacher
Title: Human Impact on Animals
Lesson: Natural Selection
Classroom Activity
Activity Directions:
Humans have a tremendous impact on domestic animal and plant manipulation. Today, our
knowledge of genetics is used to change plants and animals so they can better meet our needs.
In this activity, your teacher will place the class into groups and assign each group an animal or
plant species. Each group will research information by asking parents/teachers or by reading
books/magazines to determine different ways in which humans have had an impact on the
selected species. *For example: human impact on cattle breeds.*
After sufficient research has been completed, your group should be prepared to present their
findings.
Materials Needed:
1. Paper.
2. Resource material.
A. Biology books (i.e. Campbell)
B. Agricultural science books or animal science books (i.e. Del Mar, Interstate).
Notes to teacher:
We have suggested this activity because it allows the student to become aware of how our society
has manipulated agriculture to suite our needs. It also helps the student learn about the history of
the animal or plant assigned to him/her.
It is suggested that the students work in groups of three or four so collaboration can occur. It is
also suggested that the groups present their findings to the class. This exercise should stimulate
active class participation.
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Model Agricultural Core Curriculum: Supplement
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Name:__________________
Date:___________________
Title: Human Impact on Animals
Lesson: Natural Selection
Classroom Activity
Activity Directions:
Humans have a tremendous impact on domestic animal and plant manipulation. Today, our
knowledge of genetics is used to change plants and animals so they can better meet our needs.
In this activity, your teacher will place the class into groups and assign each group an animal or
plant species. Each group will research information by asking parents/teachers or by reading
books/magazines to determine different ways in which humans have had an impact on the
selected species. *For example: human impact on cattle breeds.*
After sufficient research has been completed, your group should be prepared to present their
findings.
Materials Needed:
1. Paper.
2. Resource material.
A. Biology books (i.e. Campbell)
B. Agricultural science books or animal science books (i.e. Del Mar, Interstate).
Notes to teacher:
We have suggested this activity because it allows the student to become aware of how our society
has manipulated agriculture to suite our needs. It also helps the student learn about the history of
the animal or plant assigned to him/her.
It is suggested that the students work in groups of three or four so collaboration can occur. It is
also suggested that the groups present their findings to the class. This exercise should stimulate
active class participation.
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Notes to the Teacher
Title: "Pips"
Lesson: Natural Selection
Laboratory
To the Teacher:
This lab introduces "Pips," a game which demonstrates basic principles of population biology
including population growth, natural selection, and evolution. The purpose of the game is to
model changes in populations over time. A series of models are outlined, each of which
demonstrates a different concept in population biology.
The game looks complex but is actually very simple. You will probably be able to think of other
models to demonstrate using the game.
Purpose:
The purpose of this laboratory is to demonstrate different aspects of natural selection using a
game called Pips. Your teacher will guide you through several different models showing how
natural selection can lead to evolution.
Materials:
1. A game board for each pair of students.
2. 3 sets of markers (pips) for each game board. Markers can be split peas, lentils, corn kernels
or other dried seeds. Do not use round beans or peas as they tend to roll off the game board.
You will need about 50 pips of each kind. Heavy duty zip-lock bags make a good storage
container for the pips.
3. One die for the entire class.
4. Student worksheets.
5. Graph paper.
6. Straight edge or ruler.
Procedure:
Run each simulation following the instructions on the worksheet. After each generation in the
simulation, record the number of pips of each kind on your data sheet. After each simulation has
been completed, graph the behavior of the population(s), and answer the questions on your
worksheet.
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Name:__________________
Date:___________________
Title: Pips
Lesson: Natural Selection
Laboratory
Purpose:
The purpose of this laboratory is to demonstrate different aspects of natural selection using a
game called Pips. Your teacher will guide you through several different models showing how
natural selection can lead to evolution.
Materials:
1. A game board for each pair of students.
2. 3 sets of markers (pips) for each game board. Markers can be split peas, lentils, corn kernels
or other dried seeds. Do not use round beans or peas as they tend to roll off the game board.
You will need about 50 pips of each kind. Heavy duty zip-lock bags make a good storage
container for the pips.
3. One die for the entire class.
4. Student worksheets.
5. Graph paper.
6. Straight edge or ruler.
Procedure:
Run each simulation following the instructions on the worksheet. After each generation in the
simulation, record on the data sheet the number of pips of each kind on the board. After each
simulation has been completed, graph the behavior of the population(s), and answer the questions
on your worksheet.
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Name:__________________
Date:___________________
Title: Pips
Lesson: Natural Selection Laboratory
Student Worksheet
Introduction
Tape the game board to the playing table so that it lies flat and will not move during the game.
Begin with one pip in the very center of the board. Pips always grow from the center outwards.
Pips are an imaginary species. You can think of them as plants or animals. In some of the
models you will be told what the pip is. Pips only have one generation per year, and the
generations are non-overlapping. This means the parents die before the young hatch or
germinate.
When the pips reproduce, the number of pips which are added to the habitat (game board)
represent the number of females in the next generation. This is a common way scientists
simplify the process of modeling population growth.
In each model the rate at which pips are born or die are given as follows:
1 --> 2
This mean that when the pips reproduce, two female offspring are produced and
survive.
2 --> 1
This means that only one pip survives for every two living in the previous
generation.
In models with mutation, your teacher will roll a die twice and call out a pair of numbers between
one and six. These numbers correspond to the row and column in which the mutation took
place. For example if the teacher calls out "one, six" then the pip in row one, column six is a
mutant.
Pips are somewhat unrealistic with respect to mutation rates and the number of successful
mutants which occur. Remember that most mutations are harmful or so small as to not affect
survival. Mutations generally occur at rate of 1 in a thousand to one in a million per cell
replication, not 1 in 36 as in pips.
The Pip Habitat has a carrying capacity of 36 Pips (one for each square). Squares are color coded
for three degrees of quality: Good (white squares), fair (light gray squares), and poor (dark
gray squares). Spare pips are placed in the circles off of the main grid.
After each generation, record on the data sheet the number of pips of each kind on the board.
The first pip is always generation zero. After each simulation has been completed, graph the
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behavior of the population(s), and answer the questions on your worksheet. For model sets 1
and 2 you can graph all the models together on the same graph.
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Model Set 1 - Exponential Growth.
1. Each pip replaces itself and adds 3 additional pips to the population.( 1-->4 ) When carrying
capacity is exceeded only one in four Pips reproduce successfully ( 4 -->1). Run the
simulation until the pip population exceed carrying capacity.
a. How many generations does it take for the pips to exceed the carrying capacity of the
habitat?
b. How many pips are there when the carrying capacity is exceeded?
c. What do you predict would happen to the pips after exceeding carrying capacity?
d. If the pips could keep growing at this rate, how many pips would there be after 6
generations?
2. Track the growth of pips with 1 --> 3 until carrying capacity is reached, and 9 --> 1 after
carrying capacity. Run the simulation for 8 generations.
a. How many generations does it take for the pips to exceed the carrying capacity?
b. What do you predict the population will be after twelve generations?
Model Set 2: Density dependent growth
1. Track the growth of pips with 1 --> 2 up to carrying capacity, and reproducing 1-->1 after
carrying capacity is reached.
a. How long do these pips take to reach carrying capacity? How do these pips compare to
those in one and two above?
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b. What do you predict the pip population will be after twelve generations
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2. These pips reproduce at different rates depending on how much of the habitat has been used.
In the white area pips reporoduce 1 --> 4; once at least one pip lives in the light gray area, all
the pips reproduce at the rate of 1 --> 2. Once one pip lives in a dark gray area, the
population grows to 36 and reproduces 1 -->1. Run the simulation for 8 generations.
a. What happens to the growth of the pip population as it approaches the carrying capacity of
the pip environment?
b. How is the shape of the graph different from the graphs you made in models 1 - 3.
c. This curve is called the logistic growth curve. Why do you think it has this name?
Model Set 3: Mutation and Natural Selection
For these models you will need to have two kinds of pips. You will also need someone to throw
the die to determine where mutations occur. Start by reproducing the first pip, then mutate,
then reproduce etc. until carrying capacity is exceeded. No mutations occur when the
population is above carrying capacity.
1. Select one pip to be the normal type and one to be the mutant. In this exercise, a mutant
mutates back to the normal type if its square is called. Normal pips reproduce 1-->3 up to
carrying capacity, and go 9 --> 1 when carrying capacity is exceeded. Mutants are better
foragers due to a slight modification in mouth parts. They reproduce 1-->3 up to carrying
capacity and go 3-->1 when carrying capacity is exceeded. Run the simulation for 8
generations.
a. What is the agent (cause) of natural selection in this model?
b. What happens to the populations of the two kinds of pips over time? Does this constitute
evolution?
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2. Normal pips grow 1 --> 2 until they reach the dark gray squares. Once one pip lives in a dark
gray area, the population grows to 36 and reproduces 1 -->1. Pip 2 grows at the same rate,
but is less susceptible to pesticides because of a certain wax in its shell. The farmer sprays
when the population reaches carrying capacity. Normal pips die at the rate of 9 --> 1 while
mutants die at the rate of 4 --> 1. Run the simulation for 10 generations, with the farmer
spraying each time the pips fill the habitat.
a. What happens to the population over time?
b. What is the agent of selection in this model?
c. Compare your results with the rest of the class, are there differences in the population
graphs? Why is this?
3. In this simulation the weather can change from year to year. Mutants are better adapted to hot
weather than are normal pips. Weather is determined for each generation by a toss of the die.
1
2-5
6
= cold year
= normal year
= hot year
In cold and normal years both normal and mutant pips grow as in 2 above. In hot years
normal pips reproduce 1-1 up to carrying capacity and go 2-->1 at or above carrying capacity.
Mutant pips are unaffected by the warm weather. Run the simulation for ten generations.
a. What is the agent of natural selection in this model?
b. At the end of the simulation, what is the ratio of mutant to normal pips?
c. Calculate the average number for each type of pip at the end of the simulation for the
entire class. How does your simulation compare with the average?
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4. Run the simulation again, as in 3 above. This time global warming has increased the
frequency of hot years. Weather is determined as shown below:
1
2-3
4-6
= cold year
= normal year
= hot year
Run the simulation for ten generations.
a. How does this simulation compare with simulation number three? What caused the
differences between the simulations?
Other Models
You may want to run other simulations using pips. One idea is to have pips mutate to the
different growth rates used in model set one: Normal pips behave as in model 1-1, the first time
a pip mutates it changes to model 1-2, the third time it mutates it changes to model 1-3, if a pip
mutates a fourth time it returns to normal (model 1-1).
You can also experiment with combinations of pips from model set 1 and model set 2. Other
possibilities are demonstrations of predation, resistance of diseases to drugs, and gene flow or
genetic drift.
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Pips Data Sheet
Data Table - Model Set 1
Number of Pips
Generation #
Model 1-1
Model 1-2
Model 1-3
1
2
3
4
5
6
7
8
Graph - Model Set 1
85
80
75
70
65
Number
of
pips
60
55
50
45
40
35
30
25
20
15
10
5
0
1
2
3
4
5
6
Generation Number
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7
8
9
10
Data Table - Model Set 2
Number of Pips
Generation #
Model 2-1
Model 2-2
1
2
3
4
5
6
7
8
Graph - Model Set 2
85
80
75
70
65
Number
of
pips
60
55
50
45
40
35
30
25
20
15
10
5
0
1
2
3
4
5
6
Generation Number
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7
8
9
10
Data Table - Model Set 3
Number of Pips
Gen. #
Model 3-1
Normal
Mutant
Model 3-2
Normal
Mutant
Model 3-3
Normal
Mutant
1
2
3
4
5
6
7
8
9
10
Graph - Model 3 - 1
85
80
75
70
65
Number
of
pips
60
55
50
45
40
35
30
25
20
15
10
5
0
1
2
3
4
5
6
Generation Number
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7
8
9
10
Model 3-4
Normal
Mutant
Graph - Model 3 - 2
85
80
75
70
65
Number
of
pips
60
55
50
45
40
35
30
25
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
7
8
9
10
Generation Number
Graph - Model 3 - 3
85
80
75
70
65
Number
of
pips
60
55
50
45
40
35
30
25
20
15
10
5
0
1
2
3
4
5
6
Generation Number
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Graph - Model 3 - 4
85
80
75
70
65
Number
of
pips
60
55
50
45
40
35
30
25
20
15
10
5
0
1
2
3
4
5
6
Generation Number
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7
8
9
10
Height
1 2 3 4 5 6
short
Speed
1 2 3 4 5 6
tall
slow
Temperature Range
1 2 3 4 5 6
cold
Moisture Range
1 2 3 4 5 6
hot
dry
Height
1 2 3 4 5 6
short
tall
cold
slow
fast
Moisture Range
1 2 3 4 5 6
hot
dry
Height
1 2 3 4 5 6
wet
Speed
1 2 3 4 5 6
tall
slow
Temperature Range
1 2 3 4 5 6
cold
wet
Speed
1 2 3 4 5 6
Temperature Range
1 2 3 4 5 6
short
fast
fast
Moisture Range
1 2 3 4 5 6
hot
dry
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wet
Pips Playing Board
1
2
3
4
5
6
1
2
3
4
5
6
Spare Pips
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Spare Pips
Lesson: Natural Selection
Bank of Questions
1. Question: What are the main sources of genetic variation in a population?
Answer: Mutation and recombination are the primary ways in which genes change.
2. Question:
How do humans impact natural selection? Give an example.
Answer:
Humans may consciously or unconsciously change the environment in
which organisms live.
3. Question:
Answer:
4. Question:
Answer:
What is evolution?
Evolution is a change in the genetic makeup of a population over time.
What is a mutation?
A mutation is a change in the DNA of an organism.
5. Question: Variation in the chromosomes occurs when an egg and sperm unite
(recombination). Why does this happen?
Answer:
Both the egg and sperm carry unique traits from the parents into one
individual. This forms an individual that varies from either parent.
6. Question:
Describe the process of natural selection.
Answer:
Because there is natural variation in genotype among members of a
species, some members may be more likely to survive than others
when environmental conditions change.
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